1. Field of the Invention.
The present invention relates to air purified respirators and a non-invasive, quantitative method for fit testing the respirator. In particular, the filtered air respirator is of the type having at least one filter for removing dust particles, for example, and/or chemical filters designed to remove chemical contaminants such as deleterious gases and particulates. Additionally, the present invention relates to air supplied respirators requiring a tight face seal between the respirator and the face of the wearer. Moreover, the present invention has utility as a respirator for filtering such substances as paint spray, smoke, dust, and military warfare agents. The invention also contemplates a preferred non-invasive quantitative method for fit testing respirators so that each respirator is fit tested to the end user, rather than the end user being fitted with a respirator which will be a model of the one to be employed.
2. Prior Art
There are basically four distinct types of respirator face mask configurations. The first type called the quarter-mask covers the mouth and nose, and the lower sealing surface of the mask is designed to be positioned between the user's chin and lower lip.
A second type of face mask respirator is called the "half-mask", which fits over the nose, around the user3 s mouth and under the user's chin. Half-masks generally seal more reliably than quarter-masks so that these type masks are preferred against more toxic materials. The quarter-masks are designed normally for use as dust respirators. The quarter-masks may also include air purifying elements or may be air supplied when employed in a toxic environment.
A third type of face mask respirator is the full face piece which covers roughly from the hairline to beneath the chin. This type of respirator offers better protection than the quarter-mask because it is capable of achieving a good seal around peripheral portions of the face which are not affected by such movements as breathing or talking. The full face respirator may include an air purifying element or may be air supplied. Additionally, this type of respirator may be used where eye protection is necessary because the purified air generally flows across the eyes of the user before it reaches the user's nose and mouth.
The fourth and last type of respirator configuration is the helmet-hood type, designed to fit over the entire head. This type includes a compressed air line which flows air to the interior of the helmet-hood. The air escapes from the helmet-hood type by percolating through and between the peripheral edge of the respirator. This type of respirator protects the head of the user, including the eyes because the helmet includes a transparent section which shields the eyes from hazardous agents. Generally, the compressed air is designed to first flow over and around the eyes of the user, and then flow downwardly to and around the mouth of the user. Excess air flowing through the helmet-hood and exhaled carbon dioxide are discharged from the helmet-hood area by flowing between the peripheral edge of the helmet-hood, or may be discharged with a conventional exhalation valve.
Each of the first three configurations of respirators generally includes one or more of the following: an air purifying element, for example, a pleated paper filter for particle removal or a chemical cartridge or canister for gas removal, an inhalation valve, and an exhalation valve.
The helmet-hood type generally does not include any of the above elements. Sometimes the helmet-hood type can include an air flow control valve to regulate the amount of air flowing into the helmet. The air can be supplied either by a positive pressure of compressed air or the air can be supplied on demand causing a slight negative pressure within the cavity volume. When the helmet-hood has a positive pressure with respect to the surrounding atmosphere, the supplied clean air forms a flowing, moving curtain which prevents dust, fumes, smoke, and chemical contaminants such as deleterious gases from flowing into the eyes and the breathing area. When air is supplied on demand to a helmet-hood type respirator, the respirator must fit tightly about the wearer to avoid drawing in air from the surrounding atmosphere.
Many different companies produce one or more of the four types of respirators. In fact, several million respirators are sold annually in the United States alone, to protect wearers from industrial and environmental contaminants. Additionally, recent concern about potential chemical warfare has motivated the military establishment to study new respirators for combat troops, and to study fit testing methods for the user of the actual respirator to be worn.
Because of the diversity in the dimensions of human faces, a single respirator cannot properly fit every person. Therefore, leaks between the respirator mask and the face are possible, particularly with the first three respirator configurations previously mentioned, thereby reducing the protection sought by the respirator. As a result, fit testing is necessary and, for many environments, legally required to determine which type, brand, and size of respirator will provide the necessary protection for the wearer. All the care that went into the designing and manufacturing of a respirator will not protect the wearer if there is an improper match between the face piece and wearer, or if improper wearing practices are employed. The latter problem may be cured by proper instruction. The former problem usually involves either quantitative or qualitative testing of several types of face mask respirators to determine the best fitting mask.
In a qualitative test, the wearer usually tests several respirators to determine which feels most comfortable and provides at least some protection through achieving a proper seal between the wearer and the respirator. In general, qualitative tests are usually fast, require no complicated, expensive equipment, and are easily performed in the field. The general disadvantages of qualitative tests are that such tests rely upon the wearer's subjective response, and thus are not entirely reliable. Moreover, a respirator that appears to fit properly during testing may not provide an adequate seal when the user grows a beard, gains weight or merely wears out the respirator, for example.
Qualitative fit tests approved by the U.S. Government and employed industrywide comprise the negative pressure test, the positive pressure test, the isoamyl acetate vpor (banana oil) test, and the irritant smoke test.
The negative pressure test consists of merely closing off the air inlet of the face mask. The air inlet is generally one or two cartridges or filters which are secured to the face mask typically by screw threads. The inlet or inlets are covered with the palms of one's hands so that no air can be drawn in through the air inlets of the mask. The tester inhales so that the face piece collapses slightly and holds his or her breath for about 10 seconds. If the face mask remains slightly collapsed and no inward leakage is detected, the respirator provides an adequate fit.
As stated previously, the subjective and non-quantitative nature of this simple test has severe drawbacks. For example, the pressure of one's palms on the filters or cartridges of the face mask would naturally cause the face mask to have a better seal around the wearer's face than normally occurs during use. Moreover, a slight deformation of the face mask may occur with a pressure of 10 to 20 centimeters of deflected water. Stronger deformation occurs at higer pressure differentials. However, normal breathing incurs a pressure of about 1 to 4 centimeters of deflected water. Consequently, the negative pressure test is employed under conditions which are not typically found in the working environment.
The positive pressure test is very similar to the negative pressure test and in general has the same advantages and disadvantages. The positive pressure test is conducted by closing off the exhalation valve of the face mask and exhaling gently into the face piece. The fit is considered to be satisfactory if a slight positive pressure can be built up inside the face piece without any evidence of outward leakage. Of course, the disadvantage of this test is again the subjective nature of the test. For example, the employees testing the face mask would not be exhaling at the same pressure. Thus, one employee may consider the mask satisfactory, while another employee may not. Moreover, a positive pressure is not normally incurred during the inhalation cycle of air purifying respirator usage.
The isoamyl acetate vapor test gives the user the opportunity to wear the face mask in a typical environmental atmosphere. Isoamyl acetate has a pleasant, easily detectable banana odor. The tester or wearer generally is positioned in an atmosphere or environment containing the isoamyl atmosphere. The face mask must include an organic vapor removing cartridge so that if the wearer or tester detects the smell of banana oil, the vapor is only due to the leakage between the wearer's face and the face mask. The atmosphere around the tester or wearer is created by saturating a piece of cotton cloth, for example, with the liquid isoamyl acetate and passing it close to the face mask near the sealing surface. Preferably, the entire test is conducted in a small booth or hood covering at least the wearer's head and shoulders. In such an enclosure, a concentration of the isoamyl acetate vapor of approximately 100 ppm is found to be adequate since most people can smell the vapor at concentration levels of about 1 to about 10 ppm. Initially, this test is conducted with the tester remaining perfectly still. If no banana odor is detected, then the test is expanded to include activities such as deep breathing, side-to-side movement of the head, up and down movement of the head, and talking loud enough to be understood by someone standing nearby. Such activities add to the dependability of the face mask since such movements often occur in the working environment.
One major drawback of the isoamyl acetate test is that the sense of smell is easily dulled and may deteriorate during testing to the extent that the wearer can only detect high vapor concentrations. Also, each individual differs from the others in the threshold detection limit, resulting in a satisfactory mask for some individuals and an unsatisfactory respirator for others, although the leakage is constant in all instances. Moreover, because isoamyl acetate has a pleasant smell, even at high concentrations, a wearer may subjectively state that the face mask fits comfortably without leakage, because of peer pressure to use a specific type mask or the comfort of the particular face mask.
The irritant smoke test is similar to the isoamyl acetate test in concept. However, instead of employing isoamyl acetate, which has a pleasant smell, an irritating aerosol produced by commercially available smoke tubes normally used to check the quality of ventilation systems is employed. Typically, the smoke tubes are filled with pumice impregnated with stannic chloride or titanium tetrachloride. When the seal of the tube is broken, the moisture in the air rects with the contents of the tube to produce a dense, highly irritating smoke consisting of hydrochloric acid. This test has a distinct advantage in that the tester reacts involuntarily to leakage by coughing or sneezing. Consequently, the likelihood of the tester or wearer giving a false indication of proper fit is greatly reduced. However, the aerosol produces extreme irritation because the hydrochloric acid tends to burn the sinus passages. Thus, great care must be exercised to avoid injury.
The irritant smoke test must be conducted in a hooded or enclosed environment where the tester initially remains stationary. If no irritating smoke is detected, the tester then proceeds to move his head from side to side, and again if no smoke is detected, to move his head up and down, and again if no smoke is detected, to talk loud enough to be understood by someone standing nearby. If the wearer still does not detect any irritating smoke, the face mask is judged to fit without excessive leakage.
A more precise way of determining the proper fit of a face mask is the quantitative test with test agents. The greatest advantage of quantitative testing with test agents is that the tests indicate face mask fit based upon a numerical number, which does not rely upon the subjective response of the wearer or tester. Such quantitative tests are employed most often when leakage must be minimized for work in highly toxic or harmful atmospheres such as nuclear radiation.
The disadvantage of quantitative fit testing with test agents is the expense of the testing equipment and the necessity of having highly trained personnel operate the equipment. Moreover, each face mask tested must be fitted with a test probe to allow sampling of the interior atmosphere of the face mask when it is properly worn. Consequently, the face mask used during testing is only a model of the face mask the tester or worker is to receive, instead of testing the actual face mask the worker is to use. Accordingly, minor nuances between the model tested and the actual face mask received could result in a poor or improper fit.
Recent studies of quantitative fit testing with test agents indicates that the position of the probe in the face mask may result in large discrepancies in the quantitative testing. The sampled agent concentration inside the face mask cavity depends on the location of the probe relative to the flow of purified air entering the respirator cavity, the location of the mouth or nose through which breathing occurs, and the location of the leak or leaks which is generally unknown. The mixing of agents inside the respirator cavity is incomplete during the generally short inhalation and exhalation periods. The measured concentration of the agent present may, therefore, not represent the true protection. This has been borne out by recent studies. See, Myer, W. R., American Industrial Hygiene Association Journal, Volume 45, No. 10, pages 681-688, 1984. For example, if the probe is positioned to the right side of the wearer's face, the results of quantitative testing with agents may not be the same as the results obtained when the probe is positioned at the left side of the face mask, or centered in the face mask. Because there is presently no standard for placement of the probe in the mask when testing, results obtained from one test cannot usually be correlated with results obtained from another test. Depending upon the location of the test probe and the location of the leak, the face mask may prove to be satisfactory in one instance and unsatisfactory in another instance. Consequently, while quantitative testing with test agents no longer relies on the subjective opinion of the wearer, it does possess certain disadvantages.
The presently employed quantitative tests measure the concentration of the test agent inside the mask cavity, i.e., between the mask and the face of the wearer, as compared to the atmosphere outside or surrounding the face mask. The types of quantitative testing conducted in industry and by the U.S. government comprise the sodium chloride test, DOP test (dioctylpthalate), the freon 12 test, and the sulfur hexafuoride test.
All presently employed quantitative testing involves placing the tester or wearer in an atmosphere containing easily detectable vapors or aerosols. Typically, the atmosphere is confined to a hood or an enclosure having a specified concentration of test agents contained therein. Leakage is expressed as a fit factor which is related to the concentration of the test agent in the atmosphere divided by the concentration of the test agent in the mask, when the mask is properly worn.
In the sodium chloride test, submicron size solid salt particles are dispersed by a nebulizer into a test chamber or hood. The penetration of the sodium chloride aerosol into the respirator is determined through a test probe inserted in the respirator and typically, the results are recorded on a strip chart. During testing, the wearer tests the face mask while remaining relatively stationary. Then, the wearer proceeds to move his head from side to side so that leakage from the work-simulated activity may also be recorded. Subsequently, the wearer oscillates his or her head up and down and then talks loud enough to be heard by one standing nearby. Test data from each of these movements for a given model of a face mask are compared against other models of face masks in order to determine the best face mask model fit. Comparison is made despite the inability to correlate results, as discussed previously.
The DOP test uses a dioctylpthalate aerosol in which the DOP particle is liquid, i.e., an oil. This test is similar to the sodium chloride test in that DOP particles are created by nebulization, for example, and are introduced into a flowing gas atmosphere in which the testing procedure described in the sodium chloride test are performed.
The freon 12 quantitative test is based upon a refrigerant gas--freon 12. However, this test is not often used because the presently available analyzing instrumentation has a very slow response time causing fluctuations in concentration of the refrigerant gas that penetrates the face mask. Again, testing procedures disclosed above are performed.
The fourth quantitative test mentioned above is based upon sulfur hexafluoride. Sulfur hexafluoride is a very stable gas and is one of the heaviest known gases having a density approximately five times that of air. The testing procedures disclosed above are performed.
In summary, the presently employed fit quantitative tests may comprise using a solid aerosol particle--the sodium chloride test; a liquid aerosol particle--the DOP test; a light refrigerant gas test--freon 12; or a heavy gas test--sulfur hexafluoride. As stated previously, the fit factor for the mask with any one of these test agents is given by or related to the concentration of the test agent in the environment divided by the concentration of the test agent within the face mask cavity.
In a presentation titled "Development And Validation Of A Simple Respirator Fit Test" by Miller which was presented at the Annual American Industrial Hygiene Conference in Las Vegas, Nev., May 19-24, 1985, Mr. Miller describes a method used by the Louisville, Ky., Metropolitan Sewer District, which he modified. In this modified method, a manometer is connected to the face mask and is observed during testing. The testing procedure calls for a worker or tester to properly don a respirator face mask, and during a period in which the tester or worker is holding his or her breath, the manometer is observed. If, after several seconds, the pressure is substantially reduced, the face mask fails the test. On the other hand, if the pressure level is not substantially reduced, the respirator passes the test. Consequently, :his method involves measuring a pressure change with time as the basis for failing or passing the fitness of a face mask or respirator.
The disadvantage of the Miller method is simply that it does not take into consideration the volume of the face mask. In other words, if the cavity between the face mask and the worker is large, and has a small leak, the face mask may easily pass the pressure versus time judgment described by Mr. Miller. On the other hand, if the face mask is a quarter size face mask, for example, and has the same total volume leakage as the full face mask, it may not pass the pressure change versus time judgment. Thus, while both face masks have the same leakage, one passes the test because it has a large face mask cavity, while the other smaller face mask fails the test because of its small face mask cavity. Another disadvantage of the Miller method is that it does not relate the rate of pressure change in the mask to a specific quantitative leak rate.
In summary, the prior art devices are inadequate to obtain a consistent fitness between a worker and a face mask that is reliable. The qualitative tests have the disadvantage that the fitness of a particular face mask is based upon subjective responses of the wearer. Moreover, the isoamyl acetate and the irritant smoke tests cannot be conducted each and every time the wearer employs the mask. With the quantitative tests, the test results are inaccurate and cannot be correlated between one test and another. Moreover, the wearer only tests a model of the actual face mask he is to use. Lastly, all the quantitative tests are very expensive. With the Miller method, the test procedure does not factor into consideration the respirator cavity volume, nor does it render a numerical fit factor. Accordingly, none of the prior art tests is satisfactory for indicating a numerical value which reliably indicates the fit of a mask on a person's face. Consequently, a need exists for a method which is inexpensive, can be quickly conducted and overcomes the problems of the prior art methods. Moreover, new embodiments for a face mask are needed which would achieve the above method and enable the wearer to test the face mask each and every time the wearer enters a highly toxic atmosphere.